1. Field of the Invention
The present invention relates to a coordinate alignment tool for a measuring X-ray CT apparatus and a coordinate measuring device. In particular, the present invention relates to a coordinate alignment tool for a measuring X-ray CT apparatus and a coordinate measuring device where the coordinate alignment tool enables coordinates for measurement data acquired by a three-dimensional coordinate measuring device (hereafter, referred to as a coordinate measuring device) and measurement data acquired by the measuring X-ray CT apparatus to be aligned easily, and where the coordinate alignment tool enables efficient measurement of external dimensions and internal dimensions with high accuracy.
2. Description of Related Art
Medical X-ray CT apparatuses were brought into practical use in the 1970s, and based on this technology, X-ray CT apparatuses for industrial products came out around the early 1980s. Since then, the industrial X-ray CT apparatuses have been used for observation and inspection of pores in improperly cast metal components, a welding issue of a welded component, a circuit pattern defect of an electronic circuit component, and the like, which are difficult to check from an external view. Meanwhile, along with a recent spread of 3D printers, demand is growing not only for the observation and the inspection of the interior of work pieces created by 3D printers, but also for 3D dimension measurement of an internal configuration and for accuracy thereof.
With respect to the above-mentioned trends in the technology, the measuring X-ray CT apparatus is spreading in areas centering on Germany (See Japanese Patent Laid-open Publication Nos. 2002-71345 and 2004-12407). In the measuring X-ray CT apparatus, a measured object is placed at the center of a rotation table and X-ray irradiation is performed while rotating the measured object.
A configuration of a generic X-ray CT apparatus 1 which is used for measurement is shown in FIG. 1. The X-ray CT apparatus 1 is configured with an enclosure 10 which shields X-rays, a controller 20, a control PC 22, and the like. The enclosure 10 includes therein: an X-ray source 12 firing X-rays 13 (shaped in a cone beam), an X-ray detector 14 detecting the X-rays 13, a rotation table 16 on which a measured object W is placed and which rotates the measured object W for CT imaging, and an XYZ displacement mechanism 18 adjusting a position or magnification of the measured object W which is projected onto the X-ray detector 14. The controller 20 controls the devices mentioned above, and the control PC 22 issues instructions from a user to the controller 20.
In addition to controlling each device, the control PC 22 includes a function to display a projection image of the measured object W which is projected onto the X-ray detector 14, and a function to reconfigure a tomographic image from a plurality of projection images of the measured object W.
As shown in FIG. 2, the X-rays 13 fired from the X-ray source 12 reach the X-ray detector 14 by passing through the measured object W on the rotation table 16. The tomographic image of the measured object W is generated by obtaining, using the X-ray detector 14, transmission images (projection images) of the measured object W in various directions while rotating the measured object W and by reconfiguring the images using a reconfiguration algorithm, such as a back projection method, a successive approximation method, and the like.
By controlling XYZ axes of the XYZ displacement mechanism 18 and a θ axis of the rotation table 16, the position of the measured object W can be displaced and an image capture range (position, magnification ratio) or an image capture angle of the measured object W can be adjusted.
While the measuring X-ray CT apparatus, which obtains the non-destructive tomographic image of the measured object, can measure the internal configuration, the measurement of the external dimensions of the measured object does not reach the accuracy of a coordinate measuring device.
Therefore, in order to meet a demand to be more accurate for the dimension measurement, a composite measurement system has been proposed in which the coordinate measuring device is installed inside the X-ray CT apparatus (Japanese Patent No. 5408873 ([0084] and FIG. 8)) or in a vicinity of the X-ray CT apparatus (Japanese Patent No. 3427046). In the composite measurement system, 3D dimensions obtained by the X-ray CT apparatus have been calibrated based on the external dimensions obtained with a measurement using the coordinate measuring device to achieve high accuracy.
Japanese Patent 5408873 ([0084] and FIG. 8) describes that a reference 50 is placed on a rotation table 60 and calibration is performed, and Japanese Patent Laid-open Publication No. 2002-55062 (claim 1, [0012], and FIG. 1) describes that a sample base 10 with a calibrating jig is mounted on a rotation table 3a, and a sample 11 is set in the center.
However, as described in Japanese Patent No. 5408873 ([0084] and FIG. 8), when the coordinate measuring device is mounted inside the measuring X-ray CT apparatus while still attempting to provide sufficient functions of the coordinate measuring device, an overall size of the apparatus increases and the mass of a lead enclosure which blocks the X-rays increases. Further, there are issues such as the necessity of taking measures to block the X-rays from reaching the coordinate measuring device or a probe.
On the other hand, when the functions of the coordinate measuring device are limited and the device is mounted, the above-noted measures can be taken, however, the range of measured objects which can be measured with high accuracy ends up decreasing.
In addition, it is necessary to conduct the measurements using the coordinate measuring device and the X-ray CT apparatus successively, and therefore, while the one is operating, the other is stopped. Accordingly, the coordinate measuring device and the X-ray CT apparatus, which are both expensive, cannot be used at the same time. This affects work efficiency, especially when the continuous measurement of mass produced work pieces is necessary.
On the other hand, when the coordinate measuring device and the X-ray CT apparatus are placed separately, both devices can be effectively used independently. However, the coordinates of both sets of measurement data need to be aligned so as to match up.
Japanese Patent No. 5408873 ([0084] and FIG. 8) and Japanese Patent Laid-open Publication No 2002-55062 (claim 1, [0012], and FIG. 1) are both for calibrating a deviation of the rotation center position of the rotation table, and are not for aligning the coordinates of the measurement data acquired by the measuring X-ray CT apparatus and the coordinates of the measurement data acquired by the coordinate measuring device.
The present invention has been conceived in order to resolve the above-noted conventional issues, and enables easy alignment of the coordinates of the measurement data acquired by the measuring X-ray CT apparatus and the coordinates of the measurement data acquired by the coordinate measuring device, and allows a highly accurate measurement of the external dimensions and the internal dimensions to be performed efficiently.